Title:
Turbine Blade for a Steam Turbine
Kind Code:
A1


Abstract:
Disclosed is a turbine blade for a steam turbine, comprising an aerofoil section and a root section and is characterized according to the invention in particular in that the aerofoil section is designed for use in a low-pressure stage of the steam turbine and contains fiber composite materials at least in regions.



Inventors:
Haje, Detlef (Görlitz, DE)
Application Number:
12/085274
Publication Date:
01/21/2010
Filing Date:
10/30/2006
Primary Class:
International Classes:
F01D5/28
View Patent Images:



Foreign References:
JPS63263204A1988-10-31
Primary Examiner:
ELLIS, RYAN H
Attorney, Agent or Firm:
SIEMENS CORPORATION (Orlando, FL, US)
Claims:
1. 1.-17. (canceled)

18. A turbine blade for a steam turbine, comprising: a root section; an airfoil section arranged on the root section, the airfoil section having a filling body arranged in a center portion of the airfoil section, wherein the aerofoil section contains, at least in regions, a composite fiber material that completely surrounds the filling body, and the region containing the composite fiber material is surrounded by a deformable moisture-impermeable protective layer that prevents the penetration of moisture into the composite fiber material during the operation of the turbine blade.

19. The turbine blade as claimed in claim 18, wherein both the aerofoil section and the root section in each case contain, at least in regions, a composite fiber material.

20. The turbine blade as claimed in claim 19, wherein the composite fiber material contains glass fibers, synthetic fibers and/or carbon fibers.

21. The turbine blade as claimed in claim 20, wherein the composite fiber material has fibers routed in the region of the aerofoil section at an angle deviating from a main axis of the turbine blade.

22. The turbine blade as claimed in claim 21, wherein the composite fiber material has fibers routed in the region of the aerofoil section at the angles with respect to the main axis selected from the group consisting of: ±15°, ±30° and ±45°.

23. The turbine blade as claimed in claim 22, wherein the aerofoil section is configured for use in a low-pressure stage of the steam turbine.

24. The turbine blade as claimed in claim 23, wherein an electrically conductive layer is arranged below the protective layer.

25. The turbine blade as claimed in claim 24, wherein, water-soluble chemical substances are arranged below the protective layer, which are chemically, optically and/or radiologically detectable in dissolved form.

26. The turbine blade as claimed in claim 25, wherein an onflow edge of the turbine blade is provided with edge reinforcement that protects against drop impacts.

27. The turbine blade as claimed in claim 26, wherein the root section has a composite fiber material and/or a metallic material contact element that makes contact with a blade root mounting in a rotor shaft of a steam turbine.

28. The turbine blade as claimed in claim 27, wherein the root section has a deflection element where a plurality of fibers of the aerofoil section are deflected, and/or a guide element, where fiber routing in the root section is diverted into a fiber routing adapted to the geometry of the aerofoil section.

29. The turbine blade as claimed in claim 28, wherein the root section is a plug root which is pluggable into a blade root mounting of a rotor shaft of the turbine in a direction which is radial with respect to the rotor shaft.

30. The turbine blade as claimed in claim 29, wherein the moisture-repelling protective layer further surrounds the root section.

31. The turbine blade as claimed in claim 28, wherein the root section is a sliding root which is pushable into a blade root mounting of a rotor shaft of the turbine in a direction essentially axial with respect to the rotor shaft.

32. A steam turbine with a turbine blade, comprising: a rotor arranged along a rotational axis of the turbine, and a turbine blade arranged on the rotor having: a root section, an airfoil section arranged on the root section, the airfoil section having a filling body arranged in a center portion of the airfoil section, wherein the aerofoil section contains, at least in regions, a composite fiber material that completely surrounds the filling body, and the region containing the composite fiber material is surrounded by a deformable moisture-impermeable protective layer that prevents the penetration of moisture into the composite fiber material during the operation of the turbine blade.

33. The steam turbine as claimed in claim 32, wherein the blade is a heatable guide vane.

34. The steam turbine as claimed in claim 33, wherein both the aerofoil section and the root section in each case contain, at least in regions, a composite fiber material.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2006/067923, filed Oct. 30, 2006 and claims the benefit thereof. The International Application claims the benefits of European application No. 05025359.0 filed Nov. 21, 2005, both of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a turbine blade for a steam turbine, with an aerofoil section and with a root section, which aerofoil section contains, at least in regions, a composite fiber material, the aerofoil section having a filling body which is arranged in the aerofoil center which is surrounded completely by the composite fiber material. The invention relates, furthermore, to a steam turbine having a turbine blade of this type.

BACKGROUND OF THE INVENTION

Turbine blades of this type, in particular turbine blades of this type designed as moving blades, are manufactured in the prior art from steel or titanium. Turbine blades in general and particularly end-stage blades are exposed as a consequence of their function to high centrifugal force stresses, since, to achieve high efficiency, they should constitute as high a flow-off surface as possible and consequently must possess a large blade length. High-strength steels are therefore used for conventional applications. Where these can no longer be employed for reasons of centrifugal force stresses, titanium blades are used, which, because of the lower density, also experience lower centrifugal force stresses. However, these blades are substantially more cost-intensive than steel blades. However, even where titanium blades are concerned, the flow-off surfaces are limited to approximately 16 m2 for full-revolution machines (50 Hz), thus entailing corresponding consequences for the blade lengths which can be achieved.

On account of the practical limitation with regard to the blade length, in the prior art the number of low-pressure streams is increased in low-pressure stages of steam turbines. This may take place, for example, by a change from single-stream to two-stream turbine stages or by using a plurality of low-pressure subturbines. The rotational speed of the turbo set may also be reduced. In this case, larger flow-off surfaces can then be utilized. However, all these measures entail sometimes considerable costs.

SUMMARY OF INVENTION

An object on which the invention is based is to provide a steam turbine with a turbine blade of the type initially mentioned, which makes it possible to have a particularly high efficiency of the steam turbine and at the same time can be operated in the steam turbine in an operationally reliable way.

EP A1 462 606, U.S. Pat. No. 3,883,267, U.S. Pat. No. 5,240,377, FR A 1 178 140 and EP A1 593 811 disclose in each case a turbine blade of the type initially mentioned. In these blades, the composite fiber material used or the corresponding layer consisting of it around the filling body is partially protected against erosion, but not against penetrating moisture, and this may cause damage particularly in the wet steam region. Measures for protection against erosion are also known from EP A1 577 422 and DE 24 50 253 A1. A complete blade consisting of composite fiber material and having a protective layer applied by electroplating is already known from DE 22 43 132 A1.

This object is achieved, according to the invention, by means of a generic turbine blade which has the features of the claims. Furthermore, the object is achieved, according to the invention, by means of a steam turbine according to the claims. The subclaims which in each case refer back contain advantageous developments of the invention.

According to the invention, therefore, composite fiber blades are used as low-pressure stage or end stage blades. In a comparison of various materials in terms of strengths, the advantage of composite fiber materials for use as end stage blade material is clearly shown. Thus, the strength in relation to the density (Rp0,2/ρ) is 115 m2/s2 for high-strength tempered steel, 221 m2/s2 for titanium, but 563 m2/s2 for the fiber-reinforced material CFK-HM. On account of the substantially higher strength of the composite fiber material, either turbine blades manufactured with conventional dimensions can be exposed to higher load or the turbine blades can be produced with a greater length. The centrifugal force stresses which in this case arise can then be readily absorbed by the turbine blade, without any loss of operational reliability, on account of the substantially increased strength/density ratio.

Owing to the high strength/density ratio of a turbine blade containing composite fiber material according to the invention, a greatly enlarged flow-off surface can be provided by the aerofoil section being designed for use in a low-pressure stage of the steam turbine in spite of the high centrifugal force stresses. This may take place, particularly, by the provision of a particularly great blade length.

The efficiency of the steam turbine can consequently be increased considerably.

In the sector of industrial turbines, for example, the use according to the invention of the composite fiber material makes it possible for turbine blade of predetermined dimension to be exposed to high load by allowing a higher counter pressure of the end stages (air condensation), by a higher permissible rotational speed of the drive turbines or by enlarging the end stage blades for drives of variable rotational speed. This likewise results in a higher efficiency of the steam turbine.

As already mentioned, for the sector of power station turbines, there is the potential for a very considerable lengthening of existing end stage blades, together with a substantial enlargement of the flow-off surfaces which can be achieved. For example, it is been possible hitherto for turbo sets of half-revolution design and having flow-off surfaces of 20 m2 per stream to be replaced with the aid of the turbine blades according to the invention by full-revolution turbo sets of identical flow-off surface. On account of the smaller overall size of full-revolution turbo sets, considerable cost saving becomes possible. Also, by the turbine blades according to the invention being used, the number of low-pressure streams can be reduced. The multi-stream power station applications, for example, one of three lower-pressure parts can be saved. Also, two-stream lower-pressure turbines can be replaced by single-stream machines, with the result that considerable cost savings can likewise be achieved. In addition, by means of the solution according to the invention, in any event a reduction in the plant overall size, with the flow-off cross section remaining the same, can be achieved.

The turbine blade according to the invention is particularly suitable for the last moving blade row of a steam turbine, but may likewise be used, according to the invention, for the last but two and, if appropriate, last but three blade row. It may likewise be combined with preliminary stage blades consisting of steel or titanium.

The aerofoil section containing, according to the invention, at least in regions, a composite fiber material, of the turbine blade according to the invention has the composite fiber material preferably at least in the outer wall region. Advantageously, the entire aerofoil section may also consist of composite fiber material. Furthermore, advantageously, in an aerofoil section which becomes more slender toward the aerofoil tip, the number of fibers in the longitudinal direction of the aerofoil section decreases.

The abovementioned object is achieved according to the invention, furthermore, by means of a generic turbine blade in which the aerofoil section contains, at least in regions, a composite fiber material, at least the region which contains the composite fiber material being surrounded by a deformable moisture-impermeable protective layer which prevents the penetration of moisture into the composite fiber material during the operation of the turbine blade. Furthermore, the object is achieved by means of a steam turbine which is provided with a turbine blade of this type.

Consequently, moisture absorption by the aerofoil section can be effectively prevented during operation in the steam turbine. Moisture absorption is an undesirable time-dependent process which may cause an increase in weight of the component and consequently a potential unbalance of the rotor. Moreover, moisture absorption of this type may give rise to a deformation of the composite fiber material and, under continuous action, to damage to the matrix and consequently to a failure of the component containing the composite fiber material. By a moisture-impermeable protective layer being provided according to the invention, the consequences listed above and putting the operational reliability of the steam turbine at risk are avoided. So that the protective layer undergoes the expected deformations of the basic material of the aerofoil section without damage or loss of its sealing function, the protective layer according to the invention is designed to be deformable. In this case, according to the invention, the protective layer is designed so as to be deformable. The protective layer does not lose its moisture impermeability over its useful life in spite of deformations, occurring during the operation of the blade, of that region of the aerofoil section which contains the composite fiber material. This may be achieved, in particular, in that the protection layer has an elastic insert region which overshoots the utilized expansion region of the basic material. In addition to the higher steam turbine efficiency made possible by the use according to the invention of the composite fiber material in the aerofoil section, the embodiment according to the invention of the turbine blade can be employed in a particularly operationally reliable way owing to the protective layer according to the invention which is moisture-impermeable.

Advantageously, the moisture-repelling protective layer surrounds the aerofoil section completely. Furthermore, it may also be expedient if the protective layer surrounds the entire turbine blade, that is to say even the blade root. In an embodiment which is advantageous according to the invention, the protective layer should be configured in such a way that a reliable adhesion of the protective layer is afforded even under the impact of drops. Furthermore, the design of the basic material of the aerofoil section should be such that continuing drop impacts cause no fatigue or spoiling of the basic material.

Furthermore, the abovementioned object is achieved, according to the invention, by means of a generic turbine blade in which both the aerofoil section and the root section in each case contain, at least in regions, a composite fiber material. Moreover, the object is achieved by means of a steam turbine which is provided with a turbine blade of this type.

As already mentioned above, by composite fiber material being used in the aerofoil section, the turbine blade can be configured with a large flow-off surface on account of the low density of the composite fiber material.

This increases the efficiency of the steam turbine. Furthermore, owing to the simultaneous use of composite fiber material in the root section of the turbine blade, a correspondingly secure and reliable anchoring of the turbine blade in the rotor shaft of the steam turbine can be ensured. Thus, in particular, fibers of the composite fiber material can be led continuously through the aerofoil section and the root section, so that the aerofoil section and the root section make a stable connection and a break-off of the aerofoil section during the operation of the turbine blade can be effectively avoided even when higher forces occur. The operation reliability of the turbine blade during operation is consequently ensured.

In order to ensure the fracture safety of the components containing the composite fiber material, the composite fiber material advantageously contains glass fibers, synthetic fibers, such as, for example, aramide fibers, and/or synthetic fibers. In particular, fiber-reinforced material CFK-HM may be used as composite fiber material.

In a further advantageous embodiment, the composite fiber material has fibers which are routed in the region of the aerofoil section at an angle deviating from a main axis of the turbine blade, in particular at the angle ±15°, ±−30° and/or ±45° with respect to the main axis. A high torsion resistance of the aerofoil section is consequently achieved. The composite fiber plies may be arranged mirror-symmetrically with respect to the aerofoil center surface, with the result that distortion is avoided.

By contrast, an asymmetric arrangement leads to distortion. This may be utilized in an advantageous alternative embodiment, if appropriate, for self-setting purposes. Owing to the nature of the arrangement of such fibers or plies, anisotropy may also be utilized, within a limited range, to achieve a directed change of the blade geometry as a function of the operational stresses.

In this respect, distortion of this type may be provided, in which the blade cascade opens in the case of rotational overspeeds, so that less energy is extracted from the flow and therefore does not contribute to further run-up. The distortion may likewise be utilized for setting an optimized flow profile as a function of the flow and of the load. Thus, for example, the blade cascade can be closed in the case of a lower throughflow and be opened correspondingly in the case of a higher throughflow.

In order to achieve an optimization of the blade in terms of cost and of rigidity, it is expedient if the aerofoil section has a filling body which is arranged in the aerofoil center and which is surrounded completely by the composite fiber material.

So that the functioning of the deformable moisture-impermeable protective layer surrounding the region having the composite fiber material can be monitored and in order to rule out a failure of the aerofoil section, it is expedient if an electrically conductive layer is arranged below the protective layer. This electrically conductive layer serves as a warning mechanism, by means of which damage to the protective layer can be detected, whereupon counter measures, such as, for example, a replacement or exchange of the affected component, or a repair of the protective layer can be carried out in due time. An electrically conductive layer of this type may be provided either individually or in pairs with an insulation layer lying between them.

In the latter instance, for the layer build-up of the aerofoil section, there is in the surface region of the latter a successive arrangement of the composite fiber material, of an electrically conductive, in particular metallic layer, of an insulation layer, of a further electrically conductive, in particular metallic layer and of the protective layer. To monitor the functioning of the protective layer, the insulation resistance with the respect to the surroundings or between the two electrically conductive layers can then be measured. Also, the electrical capacitance of the arrangement comprising the electrically conductive layer, the insulation layer and the further electrically conductive layer can be measured in order to monitor the functioning of the protective layer. If only one electrically conductive layer is provided, it is accordingly appropriate to measure the insulation resistance with respect to the surroundings or the electrical resistance of the electrically conductive layer in order to monitor the functioning of the protective layer.

In a further advantageous embodiment, below the protective layer, water-soluble chemical substances are arranged, which are detectable in dissolved form, in particular chemically, optically and/or radiologically. This measure constitutes an alternative possibility for monitoring the functioning of the protective layer. Thus, for example, the condensate of the water/steam circuit of the steam power station can be checked continuously. If the chemical substances arranged below the protective layer can be detected in it, this indicates damage to the protective layer.

In a further expedient embodiment, an onflow edge of the turbine blade is provided with edge reinforcement for protection against drop impacts. Such edge reinforcement may be provided by gluing onto the turbine blade or by laminating into the turbine blade. Also, such edge reinforcement may be produced by means of a thickened protective or intermediate layer. Furthermore, it is possible to thicken the protective layer correspondingly or to glue on or embed an additional protective component. Also, the basic component of the turbine blade itself may be configured with a turbine-like edge reinforcement. Alternatively, protection against drop impacts may be achieved by means of a laminate build-up of the turbine blade in which the fibers run in the transverse direction.

Furthermore, it is expedient if the root section of the turbine blade has a contact element for making contact with a blade root mounting in a rotor shaft of a steam turbine, the contact element containing composite fiber material and/or a metallic material. The contact element may consist selectively of composite fiber material or of metallic materials. The corresponding metallic materials should be selected such that they allow a load-bearing and dimensionally stable connection with the rotor shaft and prevent an overstressing of that composite fiber material of the blade root which surrounds the contact element. In particular, the contact element may be formed by a metallic sleeve. If the above-described deformable moisture-permeable protective layer is provided, this should advantageously be specially reinforced in the root region, particularly in the contact region, or be protected against damage by means of protective elements.

In a particularly advantageous embodiment, the root section has a deflection element, by means of which a substantial number of fibers of the aerofoil are deflected, and/or a guide element, by means of which an advantageous fiber routing in the blade root is diverted into a fiber routing adapted to the geometry of the aerofoil section. The deflection element and/or the guide element may also in each case consist of composite fiber material or of a metallic material. In particular, the contact element and the guide element or the contact element and the deflection element may in each case be formed by the same element.

Advantageously, furthermore, the root section is designed as a plug root which can be plugged into a blade root mounting of a rotor shaft of the turbine in a direction which is radial with respect to the rotor shaft. Expediently, in this case, the fibers of the composite fiber material are led around sleeves serving as contact elements. Moreover, advantageously, in a plug root of this type the aerofoil curvature can be copied in the root region by assignment to different pin positions of the plug root, so as advantageously to give rise to low deflections from the root region to the aerofoil region.

The outlay in terms of guide elements consequently remains restricted.

In an advantageous embodiment, the deformable moisture-impermeable protective layer also surrounds the root section. A penetration of moisture even into the composite fiber material contained in the root section is consequently effectively prevented. The useful life of the turbine blade can thereby be further increased.

In a further advantageous embodiment, the root section of the turbine blade is designed as a sliding root which can be pushed into a blade root mounting of a rotor shaft of the turbine in a direction which is essentially axial with respect to the rotor shaft. An essentially axial direction is to be understood as meaning that the push-in direction may deviate from the axial direction by up to ±40°. In particular, the root section has a curved configuration, the root curvature following essentially that curvature of the aerofoil section which prevails in the vicinity of the root. The transmission of force to blade slots is achieved by means of deflection and contact elements. Contact elements may also perform the function of guide elements. The outlay in terms of guide elements is consequently minimized.

In an advantageous embodiment of the steam turbine according to the invention, the latter has a device for observing the oscillation behavior of the turbine blade. A change in the characteristic frequency of the turbine blade can consequently be recognized, and this may be attributable to moisture absorption by the composite fiber material in the aerofoil section during the operation of the steam turbine. Such a change in the characteristic frequency of the turbine blade should then give cause for checking the functionality of the abovementioned deformable moisture-impermeable protective layer and, if appropriate, for repairing the protective layer, so that a failure of the component can be prevented.

In a further advantageous embodiment, the steam turbine has at least one heatable guide vane. Owing to heating, moisture on the guide vane can be evaporated, and corresponding damage to other turbine blades by drop impacts can be prevented. Alternatively, a device for sucking away wetness may also be provided on at least one guide vane.

The production of the composite fiber blades preferably takes place by means of the conventional methods, in which fibers are wound and impregnated with the matrix material or applied in the form of what are known as prepregs. They are then brought into their final form in what is known as a die, a curing of the matrix also taking place. For this purpose, contact, deflection or guide elements are optionally also introduced or applied at this early stage. It may then be necessary to machine the blades at specific locations, for example by grinding, for example in order to achieve the required dimensional stability, tolerance adherence and surface quality. Also, already mounted contact, deflection or guide elements may be machined or these elements may be applied after the shaping operation. As already mentioned above, furthermore, edge protection may be mounted, which is integrated into the blade profile by means of subsequent adapting work, such as, for example, by grinding. Afterwards, coating with the layers required for the protective layer and for the warning system is carried out. In this case, individual layers may be designed to be reinforced at specific locations in order to improve protective or reinforcing functions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of a turbine blade according to the invention are explained in more detail below with reference to the accompanying diagrammatic drawings in which:

FIG. 1 shows a view of a first exemplary embodiment of a turbine blade according to the invention,

FIG. 2 shows the section II-II according to FIG. 1,

FIG. 2a shows a first embodiment of the detail X according to FIG. 2,

FIG. 2b shows a second embodiment of the detail X according to FIG. 2,

FIG. 2c shows the detail Y according to FIG. 2,

FIG. 3a shows a part view of a second exemplary embodiment of the turbine blade according to the invention,

FIG. 3b shows the section III-III according to FIG. 3a,

FIG. 4a shows a sectional view of a third exemplary embodiment of a turbine blade according to the invention with a view in the direction of the root section of the blade,

FIG. 4b shows a sectional view of a rotor shaft of a steam turbine in the region of a shaft slot with a root section, fastened in it, of a turbine blade according to FIG. 4a, and

FIG. 4c shows the detail Z according to FIG. 4b.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows the first exemplary embodiment of a turbine blade 10 according to the invention which is configured particularly for use in a low-pressure stage of a steam turbine. The turbine blade 10 comprises an aerofoil section 12 and a root section 14 in the form of a plug root. The root section 14 has plug-in tabs 16 for a pin connection. The aerofoil section 12 is manufactured from composite fiber material 18 which contains glass fibers and/or carbon fibers.

The main fiber direction 20 runs along a main axis 21 of the turbine blade 10.

In a region near the root section 14, the aerofoil section 12 has an additional composite fiber ply 22. The additional composite fiber ply 22 contains additional fibers which run at a deviating angle with respect to the main axis 21 of the turbine blade 10, for example at an angle of ±15°, ±30° or ±45°, and are provided for stiffening the aerofoil section 12. A plurality of additional composite fiber plies 22 of this type may also be provided. In this case, these plies may be arranged mirror-symmetrically with respect to the aerofoil center surface, with the result that distortion is avoided. An asymmetric arrangement of the additional composite fiber plies leads to distortion. This may be utilized, if appropriate, for self-setting purposes.

FIG. 2 shows the section II-II in the aerofoil section 12 according to FIG. 1. This shows a filling body 24 arranged in the region of great aerofoil thickness for optimization in terms of weight and of rigidity. This filling body is surrounded by the composite fiber material 18. The turbine steam 26 flows onto the turbine blade 10 from the left according to FIG. 2. For protection against drop impacts, the onflow edge, facing the inflowing turbine steam 26, of the turbine blade 10 is provided with edge reinforcement 28. The edge reinforcement 28 is illustrated in more detail in FIG. 2c. It consists of metal and is fastened to the onflow edge 27 of the turbine blade 10 by means of an adhesive bond 40 having a run-out 42 appropriate in terms of adhesive bonding and of the composite fibers.

FIG. 2a illustrates the first embodiment of the build-up of the turbine blade 10 according to FIG. 2 in a surface region of the latter. The inner composite fiber material 18 is in this case surrounded by a first electrically conductive layer 36 in the form of a metallic layer, by an insulation layer 34, by a second electrically conductive layer 32 in the form of a metallic layer and finally by a protective layer 30. The protective layer 30 is designed to be moisture-repelling for sealing off the aerofoil section 12 with respect to liquid.

The protective layer 30 consequently prevents a penetration of moisture into the composite fiber material 18. Furthermore, the protective layer 30 is designed to be deformable such that, without any loss of its sealing function, it compensates the deformations to be expected during the operation of the turbine blade 10. The successive arrangement of the electrically conductive layer 32, of the insulation layer 34, and of the electrically conductive layer 36 serves for monitoring the functioning of the protective layer 30. For this purpose, the insulation resistance of the electrically conductive layers 30, 32 with respect to the surroundings or between the layers or the capacitance of the layer arrangement is measured, in order to ascertain whether moisture has penetrated through the protection layer 30 into the interior of the aerofoil section 12.

FIG. 2b shows a second embodiment of the build-up of the turbine blade 10 according to FIG. 2 in the surface region of the latter. Here, the composite fiber material 18 is surrounded by a layer of indication material 30 which is surrounded, in turn, by the protective layer 30. The indication material 38 is in the form of water-soluble substances which are detectable in dissolved form chemically, optically and/or radiologically. The indication material 38 consequently serves for detecting a leak in the protective layer 30. To be precise, if moisture penetrates into the interior of the aerofoil section 12, the water-soluble chemical substances of the indication material 38 are dissolved and can be detected in the condensate which has come from the steam leaving the turbine.

FIG. 3a shows a second exemplary embodiment of a turbine blade 110 according to the invention. A root section 43 adjoins an only partially shown aerofoil section 12 with composite fiber material 18. In this case, the fibers of the composite fiber material 18 are routed from the aerofoil section 12 into the root section 43 and in the latter are led around a contact and deflection element 46 in the form of a metallic sleeve, whereupon the fiber then runs back again into the aerofoil section 12. The element 46 consequently fulfills a deflection function. At the same time, it also performs a contact function in that it makes contact with a shaft slot 48 of a rotor shaft 47 of a steam turbine. Furthermore, according to FIG. 3a, the turbine blade 110 comprises what is known as a guide element 44, by means of which an advantageous fiber routing in the blade root is diverted into a fiber rooting, adapted to the geometry of the aerofoil section 12, of the composite fiber material 18.

FIG. 3b shows the section III-III according to FIG. 3a. The root section 43 is designed in the form of a plug root with plug-in tabs 45 for plugging into corresponding shaft slots 48 running transversely with respect to a longitudinal axis 50 of a rotor shaft 47. The plug-in tabs 45 are then fastened by means of plug-in pins arranged transversely to them in the shaft slots 48. Each of these plug roots 45 has one of the contact elements and deflection elements 46.

FIG. 4a illustrates a third exemplary embodiment of a turbine blade 210 according to the invention with a root section 52 in the form of a sliding root. The root section 52, which is illustrated more precisely in a sectional view in FIG. 4b, is pushed into a shaft slot 60 running in the axial direction of the rotor shaft. The root section 52 is in this case provided with a curvature, as illustrated in FIG. 4a, and has a deflection element 56, around which a substantial number of fibers of the composite fiber material 18 are led. These fibers are surrounded by a guide or contact element 54. This element initially fulfills the function of diverting an advantageous fiber routing in the root section 52 into a fiber rooting adapted to the geometry of the aerofoil section 12. Furthermore, the element 54 fulfills the function of making contact with a shaft slot 60 of the rotor shaft 58. The guide and contact element 54 surrounds the composite fiber material 18 of the root section 14 completely and is also contiguous to the composite fiber material 18 in the lower region of the fiber aerofoil section 12.

This region is illustrated more precisely in FIG. 4c. In order to cause no damage to the guide and contact element 54 or to the composite fiber material 18 in the event of deformations of the aerofoil section 12, a gap 62 between the composite fiber material 18 and the element 54 is provided.